Thursday, December 5, 2013

New paper finds Antarctic climate is within natural variability

Click to enlarge. Antarctic field camp. Courtesy: Liz Thomas

Click to enlarge. Ice core field camp close to the Pine Island Glacier. Courtesy: Liz Thomas

"The record shows that this region has warmed since the late 1950s, at a similar magnitude to that observed in the Antarctic Peninsula and central West Antarctica; however, this warming trend is not unique. More dramatic isotopic warming (and cooling) trends occurred in the mid-nineteenth and eighteenth centuries, suggesting that at present, the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past ~300 years."

To study climate over the past 3 centuries, British Antarctic Survey (BAS) researcher Dr Elizabeth Thomas and a team of Cambridge scientists analyzed stable isotopes in the ice core, which provide a record of past temperatures.

They found that climate variability in coastal West Antarctica is strongly driven by sea surface temperatures and atmospheric pressure in the tropical Pacific.

They discuss their findings in a paper entitled “A 308 year record of climate variability in West Antarctica” and published in Geophysical Research Letters. The authors report that their ice core record shows that the region warmed since the late 1950s at a rate similar to that observed in the Antarctic Peninsula and central West Antarctica.

However, the authors note that this recent warming trend is similar in magnitude to warming and cooling trends that occurred in the mid-nineteenth and eighteenth centuries in their record, indicating that in this coastal West Antarctic location the effects of human-induced climate change in recent years have not exceeded natural climate variability over the past 300 years.

Dr Thomas says, “The new ice core record was drilled on the ice divide closest to Pine Island Glacier, one of the fastest flowing outlet glaciers in West Antarctica. The new record captures climate variability in this globally important region and suggests that the warming observed here since the 1950s is not the largest in the past 300 years.”

The authors of the article are Elizabeth Thomas, Thomas Bracegirdle and John Turner of BAS, and Eric Wolff, formerly of BAS but bow of the Department of Earth Sciences, Cambridge University.

This is the second piece of research to show that there has been greater historic natural variability than previously thought in polar regions. A recent paper looking at an ice core in the Russian high Arctic found evidence of significant natural variability in the Arctic region. Seehere.

We present a new stable isotope record from Ellsworth Land which provides a valuable 308 year record (1702–2009) of climate variability from coastal West Antarctica. Climate variability at this site is strongly forced by sea surface temperatures and atmospheric pressure in the tropical Pacific and related to local sea ice conditions. The record shows that this region has warmed since the late 1950s, at a similar magnitude to that observed in the Antarctic Peninsula and central West Antarctica; however, this warming trend is not unique. More dramatic isotopic warming (and cooling) trends occurred in the mid-nineteenth and eighteenth centuries, suggesting that at present, the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past ~300 years.

“A 308 year record of climate variability in West Antarctica,” by Elizabeth R. Thomas, Thomas J. Bracegirdle, John Turner, Eric W. Wolff published in Geophysical Research Letters. Article first published online: 18 OCT 2013 DOI: 10.1002/2013GL057782